The present invention generally relates to blanking aperture arrays, methods of producing blanking aperture arrays, charged particle beam exposure apparatuses and charged particle beam exposure methods, and more particularly to a blanking aperture array which uses a shift register, a method of producing such a blanking aperture array, a charged particle beam exposure apparatus which employs such a blanking aperture array and a charged particle beam exposure method which uses such a blanking aperture array.
Recently, the integration density and functions of integrated circuits (ICs) have improved considerably, and the ICs are expected to play a major role in bringing out the technical advancement of the industry as a whole, including the use on computers, communication equipments and the like.
The gist of the IC production technology lies in the improvement of the integration density of fine patterns. The patterning limit of the photolithography is in the order of 0.3 .mu.m. However, in the case of the charged particle beam exposure which uses electron, ion or x-ray beams, it is possible to make patterns which have a size of 0.1 .mu.m or less with a positioning accuracy of 0.05 .mu.m or less. Accordingly, if it is possible to realize a charged particle beam exposure apparatus which exposes a pattern of 1 cm.sup.2 in approximately 1 second, this exposure technique will be far superior to other lithography techniques in terms of the fineness of the pattern exposed, the positioning accuracy, the quick turnaround and the reliability. In other words, when such a charged particle beam exposure apparatus is realized, it will become possible to produce 1 to 4 Gbit memories and 1M gate LSIs.
There are various types of charged particle beam exposure apparatuses. There is the point beam type which uses a beam which is formed to a spot shape, and there is the variable rectangular beam type which uses a beam with a rectangular cross section and variable size. On the otherhand, there is the stencil mask type which uses a stencil to form the cross section of the beam into a predetermined shape, and there is the type which uses a blanking aperture array to form the cross section of the beam into a predetermined shape.
The point beam type charged particle beam exposure apparatus has a poor throughput and is only used for research and development purposes. The variable rectangular beam type charged particle beam exposure apparatus has a throughput which is improved by one or two digits when compared to the throughput of the point beam type charged particle beam exposure apparatus. However, when exposing a pattern in which fine patterns in the order of 0.1 .mu.m are integrated with a high integration density, the variable rectangular beam type charged particle beam exposure apparatus still has a poor throughput. On the other hand, the stencil mask type charged particle beam exposure apparatus uses a stencil mask which has a plurality of repeating pattern transmission apertures at the part corresponding to the variable rectangular aperture. For this reason, the stencil type charged particle beam exposure apparatus is advantageous when exposing a repeating pattern, and the throughput is improved when compared to the throughput of the variable rectangular beam type charged particle beam exposure apparatus.
FIG. 1A generally shows a stencil type charged particle beam exposure apparatus. A convergent electromagnetic lens 212 is made up of a pair of convex electromagnetic lenses (not shown) having centers of spheres which match an optical axis 214. For the sake of convenience, the beam axis is referred to as the optical axis 214. One of the convex electromagnetic lenses forms a spherical surface 212a for the incoming light and the other of the convex electromagnetic lenses forms a spherical surface 212b for the outgoing light. A stencil mask 213 includes a variable rectangular transmission aperture 213a which coincides with the optical axis 214 and a plurality of repeating pattern transmission apertures 213b.
The beam incident position to the spherical surface 212a is determined by a deflection of an electrostatic deflector 211. For example, when selecting the variable rectangular transmission aperture 213a, the beam is incident to the spherical surface 213a at a position A, and the beam is similarly incident at a position B when the pattern transmission aperture 213b is selected. The incident position of the beam to the spherical surface 212a changes depending on the deflection of the electrostatic deflector 211, and the beam is transmitted through the stencil mask 213. The outgoing beam from the spherical surface 212b is returned to a path on the optical axis 214, and a pattern is transferred onto a wafer (not shown).
FIGS. 1C and 1D show examples of the mask pattern on the stencil mask which is to be transferred onto the wafer, and FIG. 1B shows an arrangement of the patterns on the mask shown in FIGS. 1C and 1D on the stencil mask 213. Patterns 213b and 213c are used as the pattern transmission apertures and are often used at connecting parts of interconnections. When drawing (exposing) the interconnections and the connecting parts thereof, the patterns 213b and 213c may respectively be used independently or used in groups as indicated by phantom lines. A pattern 213a is used as the variable rectangular transmission aperture. When the beam which is formed to have a rectangular cross section is projected in a state where the aperture 213a is matched to the beam cross section and then shifted so that the aperture 213a and the beam cross section partially overlap, it is possible to change the beam cross section. When the beam having the rectangular cross section is projected on the patterns 213b and 213c, the beam only passes within the aperture shown and the beam cross section is shaped in accordance with the respective patterns.
According to the stencil mask, the patterns can be exposed in one operation and it is possible to improve the exposure speed. However, although the stencil masks has a plurality of transmission apertures, the transfer patterns must be formed in advance as the stencil mask in accordance with the exposure. In addition, since the exposure region is finite, it is necessary to prepare a plurality of stencil mask for a semiconductor circuit which requires a plurality of patterns such that all the patterns cannot be accommodated within one stencil mask. In this case, it is necessary to use the plurality of stencils one by one, and the throughput greatly deteriorates because of the need to change the stencil mask.
As one method of eliminating the above described problems, there are proposals to use a two-dimensionally arranged blanking aperture array in place of the stencil mask. By use of the blanking aperture array, it is possible to transfer a pattern which has an arbitrary shape by simply changing signals applied to each of blanking electrodes.
According to the exposure method which employs the blanking aperture array, a large number of apertures are arranged two-dimensionally on a semiconductor crystal substrate made of silicon or the like, and a pair of blanking electrodes are formed in each of the apertures. A pattern data indicates the pattern which is to be transferred and determines those blanking electrodes which are to receive a voltage and those blanking electrodes which are not to receive a voltage. For example, when one of the pair of blanking electrodes of the aperture is grounded and the other blanking electrode receives a voltage, the electron beam which is transmitted through this aperture is bent. The bent electron beam is transmitted through a lens which is positioned below the blanking aperture array but is cut by an aperture so that the beam does not reach the wafer. On the other hand, when no voltage is applied to the blanking electrodes of the aperture, the electron beam is not bent and the electron beam is projected on the wafer via the lens and the aperture which does not cut the beam since the beam is not bent.
FIG. 2 generally shows a known electron beam exposure apparatus which employs the blanking aperture array. Only a brief description will be given of this known electron beam exposure apparatus. A blanking aperture array BAA forms the cross section of an electron beam EB into a dot pattern having a desired shape. The electron beam EB which is emitted from an electron gun EG is converged, deflected and input/output perpendicularly to the blanking aperture array BAA. The electron beam output from the blanking aperture array BAA is further converged, deflected and transmitted through an objective OL so as to be projected at a designated position on a wafer WF which is placed on a movable stage ST. The blanking aperture array BAA may be used together with the stencil having the variable rectangular aperture. In such a case, the electron beam is shifted as indicated by a phantom line so that the electron beam passes a desired position on the blanking aperture array BAA. Such shifting of the electron beam and the ON/OFF of each aperture of the blanking aperture array BAA is controlled by a pattern controller PCTL, and this pattern controller PCTL is controlled by a central processing unit CPU. In FIG. 2, MD denotes a magnetic disk apparatus, MT denotes a magnetic tape apparatus, D/A denotes a digital-to-analog converter, and G/S denotes a two-dimensional ON/OFF information generating/storing apparatus.
For example, the two-dimensional blanking aperture array comprises 200.times.200 apertures, and the electron beam which is transmitted through these apertures is formed into a maximum of 200.times.200 point beams. Because the apertures can be turned ON/OFF independently, it is possible to describe an arbitrary two-dimensional figure by the 200.times.200 dots. The electron beam which is transmitted through the blanking aperture array is reduced by a lens and is projected on the wafer in a region of 4 .mu.m.times.4 .mu.m as a maximum of 200.times.200 beams with the dot size of 0.01 .mu.m, for example. Because the spherical abberation and chromatic aberration of the final lens of the electron beam exposure apparatus can only be suppressed to approximately 0.02 .mu.m, the independent beams which are obtained via the blanking aperture array may make contact or overlap each other. As a result, the exposed and developed patterns will not include separated independent points.
It is, however, not easy to apply ON/OFF information to the blanking electrodes of 40,000 (200.times.200) apertures of the blanking aperture array. For example, apertures of 10 .mu.m.times.10 .mu.m are etched and formed with a pitch of 15 .mu.m in a silicon (Si) substrate having a thickness of 30 .mu.m, and a thin oxide layer in the order of 3000 .ANG.is formed on the surface of the Si substrate. When a tungsten (W) layer is formed on the two mutually confronting surfaces in each aperture so as to form the blanking electrodes, a lattice portion having a width of 5 .mu.m is formed on the Si substrate. Metal interconnection patterns must be formed on this lattice portion which has the width of 5 .mu.m, so that an electrical signal can be applied independently to the blanking electrodes of each of the apertures. In this case, it is necessary to form at least 100 interconnection patterns in each horizontal line of the lattice portion, assuming that the interconnection patterns are formed independently from the two sides of the Si substrate for the right and left sides. In order to form a line-and-space pattern within the width of 5 .mu.m with one interconnection level, it becomes necessary to form a line-and-space pattern of 0.025 .mu.m at the most packed part of the interconnection but such a fine line-and-space pattern cannot be realized at the present. Even when the multi-level interconnection is employed, it is still necessary to form a line-and-space pattern of 0.25 .mu.m when ten interconnection levels are used. Although the line-and-space pattern of 0.25 .mu.m can be realized technically, it is unrealistic at the present to provide ten interconnection levels.
The blanking aperture array also suffers from the following difficulties. That is, the blanking aperture array is normally set in a vacuum called a column within the electron beam exposure apparatus, however, it is virtually impossible to connect 40,000 signal lines into the column when taking into account the signal transmission lines, the IC for sending the signals and the hermetic sealing for the vacuum. Accordingly, the two-dimensional blanking aperture array is impractical when the extremely large number of interconnections are to be formed for the purpose of independently supplying the ON/OFF information to the blanking electrodes of each of the apertures.
Furthermore, the blanking aperture array also introduces problems in beam correction. When correcting the irregular intensity at each cross section of the beam incident to the blanking aperture array, that is, when correcting the non-uniformity of the intensity distribution of the crossover image, the ON time of each aperture is corrected accordingly. However, in the case of an n.times.m two-dimensional blanking aperture array having an extremely large number of apertures, a correction circuit for correcting the ON information to be supplied to each of the apertures becomes complex and large scale.
On the other hand, when the patterns become extremely fine, the thickening/thinning of the patterns due to proximity of adjacent patterns becomes conspicuous. The proposed exposure apparatus, however, does not have a means for correcting the proximity.
An exposure apparatus which uses the two-dimensional blanking aperture array of the type described above is proposed in a Japanese Laid-Open Utility Model Application No. 56-19402. This proposed exposure apparatus employs an aperture array which is made up of a plurality of gate plates so as to distribute the interconnections to the blanking electrodes over the plurality of gate plates. However, the interconnections to the blanking electrodes are still complex because the number of interconnections as a whole is not reduced. In addition, it is extremely difficult to position the corresponding blanking electrodes between the gate plates.
On the other hand, a one-dimensional blanking aperture array having a single row of apertures eliminates the above described problems related to the interconnections. For this reason, the one-dimensional blanking aperture array can be produced by simple production steps. However, the throughput of the one-dimensional blanking aperture array is small, and it is impossible to satisfy the demands of IC production such as drawing 1 cm.sup.2 on the wafer in 1 second.